With the increase in integration of a semiconductor device, a pattern formed in a production process of the semiconductor device is miniaturized, and a shape dimension of the pattern is required to be managed and measured with high accuracy.
Representative means for measuring the shape dimension of the pattern includes a spectroscopic ellipsometry method using visible light or UV light, a critical dimension secondary electron microscope (CD-SEM) method using an electron beam, and the like.
The spectroscopic ellipsometry method is used to measure a shape dimension in a vertical direction with respect to a wafer surface such as a film thickness of a deposited film or a process film. Meanwhile, the CD-SEM method is used to measure a shape dimension in a horizontal direction with respect to the wafer surface such as a process line width or critical dimension (CD).
In the case of a measurement of a film thickness of a film which is not likely to transmit the visible light and UV light such as a trench process shape to form a STI (Shallow Trench Isolation) structure, a transistor shape and a wiring film thickness, and a measurement of a shape dimension having a three-dimensional structure, it is hard to measure them with high accuracy by the spectroscopic ellipsometry method or the CD-SEM method. For example, as shown in FIG. 7, in the case of a measurement of a third-dimensional shape in which a silicon oxide film 902, and a silicon nitride film 903 are sequentially formed on a semiconductor substrate 901, and a trench 904 to be filled with an insulation film is formed in the STI region, a high-accuracy measurement cannot be made by the spectroscopic ellipsometry method or the CD-SEM method.
Thus, an atomic force microscope (AFM) method, or a cross section secondary electron microscope (X-SEM) method is used when such a three-dimensional shape is measured.
However, these methods are low in throughput and performed through a contact or destructive inspection, so that cost required for a management of a production process problematically increases.
One of the means to solve the problem includes a scatterometry method (light-wave scattering measurement method) using a light wave. For example, Patent Document 1 discloses a principle to measure a shape dimension of a pattern by the scatterometry method. In addition, Patent Document 2 discloses a method to measure a shape dimension of a surface of a semiconductor device.
According to the scatterometry method, a repeat pattern provided with lines and spaces alternately is irradiated with a measurement beam, and shape dependency characteristics of the repeat pattern of reflected light in a light wavelength band are calculated by numerical analysis, and a three-dimensional shape of the pattern is found by comparing it with an actual measurement value.
Specifically, the scatterometry method uses the fact that when a measurement beam is obliquely applied to a surface of a semiconductor wafer, and the measurement beams are applied from various angles with respect to an angle α which is an in-plane rotation direction containing the wafer surface, spectrums of reflected and diffracted light change according to the three-dimensional pattern shape of the surface of the semiconductor wafer (see FIG. 8).
In this case, theoretical spectrums for a plurality of model pattern shapes are simulated and put in a library management. Thus, by comparing it with actual spectrum obtained from the surface of the semiconductor wafer, that is, by performing fitting, a three-dimensional shape of the closest model pattern is extracted as a measurement value.
With this method, the wafer can be measured in a nondestructive and non-contact manner under air pressure with a high throughput.
For example, in the case of the pattern shape shown in FIGS. 7 and 8, parameters which determine the three-dimensional shape include a pattern line width (CD1) 911, a space line width (CD2) 912, a substrate trench depth 921, a silicon oxide film thickness 922, a silicon nitride film thickness 923, and a tapered angle 931.
When the three-dimensional shape is measured by the scatterometry method, an inspection region 941 having a repeat pattern having identical line widths and identical space widths as shown in FIG. 8 is laid out on the semiconductor wafer, the inspection region 941 is irradiated with a measurement beam (white incident light) 951 at an incident angle of θ, and spectrums of reflected and diffracted light 952 are obtained with respect to a plurality of angles α. Thus, by fitting the obtained measurement result to the three-dimensional shape of the model pattern, the parameters 911, 912, 921 to 923, and 931 are determined at the same time, and these values are set to the measurement values of the three-dimensional shape.
Meanwhile, the three-dimensional shape to be measured in the surface of the semiconductor wafer is not completely unpredictable, and actually it is limited to some extent with respect to each production process.
Therefore, Patent Document 3, for example discloses a method to facilitate the fitting performed when a resist shape is measured by previously simulating an assumed change of the resist shape as a model pattern and putting in a library management, with respect to fluctuation of a process parameter which is predicted in a lithography step.
In addition, Patent Document 4 improves fitting validity by previously creating a test sample having fluctuated parameters which are predicted in a production step, and putting spectrum data obtained from the test sample and three-dimensional shape data obtained by measuring the test sample according to another method (such as AFM method) in a library management.
Furthermore, Patent Document 5 discloses a method to measure a three-dimensional shape using both of the AFM method and the scatterometry method, and Patent Document 6 discloses a method to obtain height information of a pattern by the scatterometry method and to measure a three-dimensional shape using the height information by the CD-SEM method.